The present invention relates to a method of and apparatus for measuring the life of foam on a non-opaque liquid. More particularly this invention is concerned with the measurement of the life of the foam head on an effervescent liquid.
In the manufacture of effervescent beverages, whether artificially carbonated or naturally fermented, it is frequently necessary to know the exact life of the foam on the beverage in order to control the production. This is particularly the case in the brewing of beer where the head is an important aspect of the product, and is also indicative of the effervescence of the product.
In a brewery this is typically done by carefully withdrawing or dipping-out a quantity of beer so as to avoid formation of foam. Then a predetermined quantity of this beer is poured into a graduated vessel and a laboratory assistant times with a stopwatch the interval before the head shrinks to a predetermined level. With this system the considerable difficulty is that it is almost impossible to accurately reproduce the results, as the method of pouring, and the operator's particular sensibilities enter into the measurement of the foam life.
It has been suggested to add a quantity of ground carbon powder to the beer in order artificially to cause the formation of a head on the surface on the quantity of beer. The height of the head thus formed is a good indication of the effervescence of the product. However, this method has the considerable disadvantage that it is almost impossible to reproduce the results accurately, as the exact granularity and density of the carbon powder often change from batch to batch. Furthermore, this system has the disadvantage that it is in effect using an unnatural system for producing the foam, and in addition it renders the beer altogether opaque afterward. Thus, this method has not achieved large commercial success.
A so-called Ross and Clark method allows the relatively accurate determination of the stability of the foam by means of a logarithmic formula. In accordance with this method, a predetermined quantity of beer which has sat for approximately one minute is allowed to pour down into a vessel. As soon as the vessel is filled a stopwatch is started and after a predetermined time a quantity of the beer is removed from the vessel. To the foam that remains in the vessel 2 milliliters of amyl alcohol is added in order to transform this quantity of foam into a predetermined quantity of liquid. In accordance with this method the stability of the foam can be ascertained by the formula: ##EQU1## wherein: S = the stability
t = time the foam is allowed to be reabsorbed, PA1 b = the amount of beer withdrawn, and PA1 c = the volume in milliliters of beer left after addition of the amyl alcohol.
This last-mentioned method gives relatively accurate results, but still it is difficult exactly to reproduce the measuring parameters and similarly it is necessary to use a highly qualified laboratory person to carry out each test. Thus the considerable cost necessary to obtain these measurements is not justified due to their relative inaccuracy.